Sharpness is a perceptual feature, which is determined by the human visual system. While the human eye is more sensitive to the sharpness of the luminance signal than to that of the chrominance, higher resolution images such as high definition television (HDTV) images, require the co-joint enhancement of both the luminance (black and white) and the chrominance sharpness. In color television broadcasting standards, such as National Television System Committee (NTSC) and Phase Alteration by Line (PAL), for example, the limited bandwidth of the chrominance and the luminance signals produces relatively slow transitions, causing smeared edges in the received images.
Various methods for sharpness enhancement have used edge transition to better improve the picture quality, but either lacked adaptability to the picture contents, degraded with noisy sequences and/or required complex hardware. Even though improving the edge transitions results in an improved overall sharpness, the lack of adaptability to the picture contents produces irritating artifacts and reduces the overall impression of sharpness improvement.